1. Field of the Invention
The present invention relates to processing digital video streams and, more particularly, to a method and apparatus for determining a transport bit rate for a multiprogram transport stream (MPTS).
2. Description of the Background Art
Commonly, transport streams carrying compressed digital content (e.g., audio/video/data) are transmitted from a source (e.g., uplink or headend) towards receiving equipment over a packet-based network (e.g., Ethernet network). Due to variable transmission delays through the network, individual transport stream packets suffer from variable delays at the receiving equipment, which is referred to as “jitter.” Jitter deleteriously affects the processing and decoding of the content carried by the transport stream packets. As such, the receiving equipment must compensate for the jitter before distributing the transport stream packets to user terminals.
Typically, multiple content streams (“programs”) are multiplexed to form a single transport stream, which is then transmitted towards the receiving equipment. For example, several MPEG (Moving Picture Experts Group) programs, such as MPEG-2 programs, may be multiplexed to form a multi-program transport stream (MPTS). One technique for de-jittering an MPTS is to buffer the received packets and then send them out at a steady output rate. This de-jittering technique requires the original transmission rate (“bit rate”) of the MPTS. However, upon initially receiving an MPTS, an accurate determination of the original bit rate of the MPTS is often difficult to obtain within a short period of time. This is due to the jitter introduced by the network.
Moreover, an MPTS often contains programs having different time bases (known as program clock references (PCRs)). Within the MPTS, each time base may vary by up to a particular tolerance level (e.g., ±30 parts per million (ppm) for MPEG-2). If the initial bit rate selected for the de-jittering process is in error from the actual bit rate, some of the outlying PCR time bases may exceed the specified tolerance after the de-jittering process. Accordingly, there exists a need in the art for a method and apparatus for determining an initial transport stream bit rate for use in de-jittering an MPTS such that no PCR time base within the MPTS exceeds a specified tolerance.